Mobile devices, such as mobile phones, are often provided with a location unit able to determine its current location either on the basis of satellite signals (i.e. GPS location system), or by any other position determination technology, such as positioning got by triangulation procedure with mobile phone antennas. By transmitting the location of a mobile phone onto a television system, it becomes possible, e.g. for friends or family members of the mobile phone user, to know where this user is and to track him, for instance on a map displayed on the TV screen, without calling him on his mobile phone.
For this purpose, the document US 2006/0103551 discloses a system for tracking a mobile unit with a GPS system and for displaying an electronic map on a displaying unit. The position data of the mobile unit is transmitted to a master control station. The user of the displaying unit needs to transmit the identifier (ID) of the mobile unit to the master control station, and then the latter transmits the position of the mobile unit to the displaying unit to show the user where the mobile unit has been located.
The document US 2006/0225108 discloses another system for communicating between a television device and one or more mobile stations in view to show the location of each mobile station on a map displayed on a screen of the television device. The television device is coupled to a broadcast network head-end and the latter couples the television device to a group communication server via Internet. The group communication server is coupled to a wireless network and collects and populates a message list table with new messages coming from the mobile device to be tracked. The server handles television device requests and responses. When receiving a location request from the television device, the server checks if the television device has the required rights for accessing to location information. If the access is granted, the location information is requested to the mobile device which sends its location to the group communication server.
The document EP1631107 discloses a method for access control between a control module and an autonomous locating module. The control module can be a personal computer of a user wanting to know the position of the autonomous locating module. The method involves sending a message containing an encrypted control value to the autonomous module. The latter checks this control value at each time it receives a message. This control value is generated by the control module and is sent to the autonomous locating module together with the identifier of the autonomous location module and with at least one command within an encrypted message. After having decrypted the message by means of a secret key, the mobile device executes the command only if the identifier and the control value are correct.
The location solutions suggested by these documents suffer from several drawbacks. For instance, some documents do not suggest any means for preventing a hacker to intercept a message comprising the location information sent by the mobile device in response to a location request message. Some systems disclose a master control station used for storing location information and dispatching them upon request from a user without worrying whether location information are outdated or have been recently acquired. In another case, the mobile device does not have any control onto the data referring to its location with respect to a user sending it a location request message via a server. Furthermore, message handling operations, performed both by the sender and the receiver, require significant computer resources which are not optimized.